The present invention relates to a ferromagnetic material sputtering target for use in the deposition of a magnetic thin film of a magnetic recording medium, and particularly of a magnetic recording layer of a hard disk adopting the perpendicular magnetic recording system, and to a sputtering target which is able to obtain stable electrical discharge when sputtered with a magnetron sputtering device.
In the field of magnetic recording as represented with hard disk drives, a material based on Co, Fe or Ni as ferromagnetic metals is used as the material of the magnetic thin film which is used for the recording. For example, Co—Cr-based or
Co—Cr—Pt-based ferromagnetic alloys with Co as its main component are used for the recording layer of hard disks adopting the longitudinal magnetic recording system.
Moreover, composite materials of Co—Cr—Pt-based ferromagnetic alloys with Co as its main component and nonmagnetic inorganic matter are often used for the recording layer of hard disks adopting the perpendicular magnetic recording system which was recently put into practical application.
A magnetic thin film of a magnetic recording medium such as a hard disk is often produced by sputtering a ferromagnetic material sputtering target having the foregoing materials as its components in light of its high productivity.
As a method of manufacturing this kind of ferromagnetic material sputtering target, the melting method or powder metallurgy may be considered. It is not necessarily appropriate to suggest which method is better since it will depend on the demanded characteristics, but a sputtering target made of ferromagnetic alloys and nonmagnetic inorganic particles used for the recording layer of hard disks adopting the perpendicular magnetic recording system is generally manufactured with powder metallurgy. This is because the inorganic particles need to be uniformly dispersed within the alloy substrate, and this is difficult to achieve with the melting method.
For example, proposed is a method of performing mechanical alloying to alloy powder with an alloy phase produced with the rapid solidification method and powder configuring a ceramic phase, uniformly dispersing the powder configuring the ceramic phase in the alloy powder, and molding this by way of hot press to obtain a sputtering target for a magnetic recording medium (Patent Document 1).
The target in the foregoing case has an appearance where the substrate is bonded in the form of soft roe (cod fish sperm) and surrounded by SiO2 (ceramics) (FIG. 2 of Patent Document 1) or dispersed in the shape of thin strings (FIG. 3 of Patent Document 1). Although the other drawings are unclear, it is assumed that they show similar structures.
These structures entail the problems described later, and are not considered to be favorable sputtering targets for a magnetic recording medium. Note that the spherical substance shown in FIG. 4 of Patent Document 1 is mechanical alloying powder, and not a target structure.
Moreover, even if alloy powder produced with the rapid solidification method is not used, a ferromagnetic material sputtering target can be prepared by preparing commercially available raw material powders for the respective components configuring the target, weighing these raw material powders to the intended composition, mixing the powders with well-known methods by using a ball mill or the like, and molding and sintering the mixed powder by way of hot press.
There are various types of sputtering devices, but a magnetron sputtering device comprising a DC power source is broadly used in light of its high productivity for the deposition of the foregoing magnetic recording film. This sputtering method makes a positive electrode substrate and a negative electrode target face each other, and generates an electric field by applying high voltage between the substrate and the target under an inert gas atmosphere.
Here, the sputtering method employs a fundamental principle where inert gas is ionized, plasma composed of electrons and positive ions is formed, and the positive ions in this plasma collide with the target (negative electrode) surface so as to discharge the atoms configuring the target. The extruded atoms adhere to the opposing substrate surface, wherein the film is formed. As a result of performing the sequential process described above, the material configuring the target is deposited on the substrate.
[Patent Document 1] Japanese Published Unexamined Patent Application No.H10-88333